Transistors such as metal oxide semiconductor field effect transistors (MOSFETs) or simply field effect transistors (FETs) or MOS transistors are the core building blocks of the vast majority of semiconductor integrated circuits (ICs). A FET includes source and drain regions between which a current can flow through a channel under the influence of a bias applied to a gate electrode that overlies the channel. Some semiconductor ICs, such as high performance microprocessors, can include millions of FETs. For such ICs, decreasing transistor size and thus increasing transistor density has traditionally been a high priority in the semiconductor manufacturing industry. Transistor performance, however, must be maintained even as the transistor size decreases.
A FINFET is a type of transistor that lends itself to the dual goals of reducing transistor size while maintaining transistor performance. The FINFET is a three dimensional transistor formed in a thin fin that extends upwardly from a semiconductor substrate. Transistor performance, often measured by its transconductance, is proportional to the width of the transistor channel. In a FINFET the transistor channel is formed at least along the vertical sidewalls of the fin, so a wide channel, and hence high performance, can be achieved without substantially increasing the area of the substrate surface required by the transistor.
Many FINFET ICs are fabricated on semiconductor-on-insulator (SOI) substrates because of the easy isolation provided by the buried oxide layer. SOI substrates are expensive, however, so there are significant economic advantages to fabricating the ICs on bulk wafers. A number of techniques have been attempted to provide isolation between fins of a bulk wafer FINFET IC, but such attempts have had limited success. Among the disadvantages of such isolation techniques are processing difficulties, complicated processing, and, most importantly, variability of the final height of the fin. The height of the fin determines the width of the transistor channel which, in turn, determines the drive capability of the transistor. Variability in fin height thus makes it difficult to reproducibly fabricate transistors having the device characteristics needed for the circuit being implemented.
Accordingly, it is desirable to provide methods for fabricating FINFET ICs having fins of predetermined and reproducible height. In addition, it is desirable to provide methods for fabricating FINFET ICs having dielectric isolation between fins. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.